net: avoid infinite recursion in Windows Resolver.lookupTXT

For #33097

Change-Id: I6138dc844f0b29b01c78a02efc1e1b1ad719b803
Reviewed-on: https://go-review.googlesource.com/c/go/+/412139
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/net/lookup_windows.go

@@ -329,7 +329,7 @@ func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
 
 func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
 	if r.preferGoOverWindows() {
-		return r.lookupTXT(ctx, name)
+		return r.goLookupTXT(ctx, name)
 	}
 	// TODO(bradfitz): finish ctx plumbing. Nothing currently depends on this.
 	acquireThread()

src/net/lookup_windows_test.go

@@ -6,6 +6,7 @@ package net
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -26,104 +27,117 @@ func toJson(v any) string {
 	return string(data)
 }
 
+func testLookup(t *testing.T, fn func(*testing.T, *Resolver, string)) {
+	for _, def := range []bool{true, false} {
+		def := def
+		for _, server := range nslookupTestServers {
+			server := server
+			var name string
+			if def {
+				name = "default/"
+			} else {
+				name = "go/"
+			}
+			t.Run(name+server, func(t *testing.T) {
+				t.Parallel()
+				r := DefaultResolver
+				if !def {
+					r = &Resolver{PreferGo: true}
+				}
+				fn(t, r, server)
+			})
+		}
+	}
+}
+
 func TestNSLookupMX(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 
-	for _, server := range nslookupTestServers {
+	testLookup(t, func(t *testing.T, r *Resolver, server string) {
-		mx, err := LookupMX(server)
+		mx, err := r.LookupMX(context.Background(), server)
 		if err != nil {
-			t.Error(err)
+			t.Fatal(err)
-			continue
 		}
 		if len(mx) == 0 {
-			t.Errorf("no results")
+			t.Fatal("no results")
-			continue
 		}
 		expected, err := nslookupMX(server)
 		if err != nil {
-			t.Logf("skipping failed nslookup %s test: %s", server, err)
+			t.Skipf("skipping failed nslookup %s test: %s", server, err)
 		}
 		sort.Sort(byPrefAndHost(expected))
 		sort.Sort(byPrefAndHost(mx))
 		if !reflect.DeepEqual(expected, mx) {
 			t.Errorf("different results %s:\texp:%v\tgot:%v", server, toJson(expected), toJson(mx))
 		}
-	}
+	})
 }
 
 func TestNSLookupCNAME(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 
-	for _, server := range nslookupTestServers {
+	testLookup(t, func(t *testing.T, r *Resolver, server string) {
-		cname, err := LookupCNAME(server)
+		cname, err := r.LookupCNAME(context.Background(), server)
 		if err != nil {
-			t.Errorf("failed %s: %s", server, err)
+			t.Fatalf("failed %s: %s", server, err)
-			continue
 		}
 		if cname == "" {
-			t.Errorf("no result %s", server)
+			t.Fatalf("no result %s", server)
 		}
 		expected, err := nslookupCNAME(server)
 		if err != nil {
-			t.Logf("skipping failed nslookup %s test: %s", server, err)
+			t.Skipf("skipping failed nslookup %s test: %s", server, err)
-			continue
 		}
 		if expected != cname {
 			t.Errorf("different results %s:\texp:%v\tgot:%v", server, expected, cname)
 		}
-	}
+	})
 }
 
 func TestNSLookupNS(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 
-	for _, server := range nslookupTestServers {
+	testLookup(t, func(t *testing.T, r *Resolver, server string) {
-		ns, err := LookupNS(server)
+		ns, err := r.LookupNS(context.Background(), server)
 		if err != nil {
-			t.Errorf("failed %s: %s", server, err)
+			t.Fatalf("failed %s: %s", server, err)
-			continue
 		}
 		if len(ns) == 0 {
-			t.Errorf("no results")
+			t.Fatal("no results")
-			continue
 		}
 		expected, err := nslookupNS(server)
 		if err != nil {
-			t.Logf("skipping failed nslookup %s test: %s", server, err)
+			t.Skipf("skipping failed nslookup %s test: %s", server, err)
-			continue
 		}
 		sort.Sort(byHost(expected))
 		sort.Sort(byHost(ns))
 		if !reflect.DeepEqual(expected, ns) {
 			t.Errorf("different results %s:\texp:%v\tgot:%v", toJson(server), toJson(expected), ns)
 		}
-	}
+	})
 }
 
 func TestNSLookupTXT(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 
-	for _, server := range nslookupTestServers {
+	testLookup(t, func(t *testing.T, r *Resolver, server string) {
-		txt, err := LookupTXT(server)
+		txt, err := r.LookupTXT(context.Background(), server)
 		if err != nil {
-			t.Errorf("failed %s: %s", server, err)
+			t.Fatalf("failed %s: %s", server, err)
-			continue
 		}
 		if len(txt) == 0 {
-			t.Errorf("no results")
+			t.Fatalf("no results")
-			continue
 		}
 		expected, err := nslookupTXT(server)
 		if err != nil {
-			t.Logf("skipping failed nslookup %s test: %s", server, err)
+			t.Skipf("skipping failed nslookup %s test: %s", server, err)
-			continue
 		}
 		sort.Strings(expected)
 		sort.Strings(txt)
 		if !reflect.DeepEqual(expected, txt) {
 			t.Errorf("different results %s:\texp:%v\tgot:%v", server, toJson(expected), toJson(txt))
 		}
-	}
+	})
 }
 
 func TestLookupLocalPTR(t *testing.T) {